Apparatus for muffling sound.



F. c. MOCK.

APPARATUS FOR MUFFLING SOUND.

APPLICATION FILED JUNE 15. 1910.

Patentd June 22, 1915.

2 SHEETSSHEET 1.

F. C. MOCK.

APPARATUS FOR MUFFLING SOUND.

APPLICATION FILED JUNE 15. 1910.

Patented June 22, 1915.

2 SHEETS-SHEET 2.'

Mar/36:4

UN TED STATES-PATENT OFFICE. J

ran-N1: c.- Mo-cx. Ore-CLEVELAND, onro.

arranarus ren mnrF-Lme sounn.

Specification 5: Letters Patent.

Patented June 22, 1915.

a n ationilea June 15, 1910. Serial No. 566,917.

To all whom it may concern;

Be it known that I, FRANK C. Moox, a citizen of the United States, and aresident of Cleveland, county," of Cuyahoga, and

5 State of Ohio, have. invented a new and useful Improvement inApparatus for Muffling Sound, of which the following is a specification,the principle of the invention being herein explained and the best modein v which I have contemplated applying that principle, so as todistinguish it from other.

inventions.

"The present invention relates to an improved apparatus for mufllingsounds, which may find application in a variety ,of uses but forillustrative purposes is shown in the form of a mufiier to silence theexplosion," of an. internal combustion engine.

The object of the present improvements is to provide such an apparatusor device which will be adapted to diminish the sound resulting from theexhaust of the motor or similar source to any desired degree withoutinterposing' obstructions of any sort in the path of the dischargedgases. Although ape paratus designed for this purpose are at present ingeneral use, and in appearance are somewhat similar ,to my improved ap-'paratus, yet they differ in details which are most important and operateupon an entirely different principle.

To the accomplishment of the foregoing and related ends, said invention,then, consists of the steps; and means hereinafter lfully described andparticularly pointed out a in the claims.

The annexed drawings and the folldwing.

- i4, 4, and 5 respectively illustrate in broken:

section different forms of muflier designed primarily for use withexplosive motors.

As of probable assistance in understanding my invention as illustratedin the a lratus shown herewith, I should first further explain theprinciple ofoperation involved. 1

There are two theories commonly advanced in explanation of the manner inwhich a sound wave is generated from the pressure energy of confined gassuddenly released from confinement, as in'the case of an ex-- plosionmotor,- a gun or the like, both of which. I believe, can be shown to beerroneous. The first of such theories is that the sound heard from anunmuflied motor for example, is produced by the exhaust issuing from themouth of the pipe and striking the,

atmosphere, thus generating the sound wave.

Hence it is assumed that by obstructing and constricting the flow of thegas it may be retarded so that it will strike the atmosphere withgenerally decreased velocity and diminished sound effect. Now, in orderto produce an audible impulse, such escaping gas would have to possessthe velocity of sound when it strikes the outside air furthermore, thisair should come to rest after each blow or the sounds will become lessand or frequency less as the speed of the motor, of discharge,increases. As a matter of fact, the sounds are known-to be individual'for each explosion up to the highest motor speed, and to accelerate acolumn of air of of sound in the small interval between two explosions,one-twentieth of a second apart, would require so much power that" thishypothesis would seem obviously wrong. Another theory not requiringdiscussion, is that the discharge of gas into the exhaust pipe sets upsome sort of sound waves which, if properly handled, may be made tointerfere with each other and so dampen out the noise of the exhaust.

It is believed that a truer explanation of any appreciable volume uptothe velocity the phenomenon is that there is but a single wave impulsefor each explosion and that such impulse is generated when the gas fromthe cylinder, rushing through the exhaust Y valve orifice at a greatervelocity than that of. sound in air, strikes the first molecules of airin the pipe; that such wave passes-out of the exhaust pipe with-thevelocity of sound. (or greater atfirst) and thenspreads through the airas does any wave impulse through any elastic medium. The travel'of thiswave impulse, however, is not quite I similar to the flow of gas whichit initiates, but differs therefrom in several important particulars. Itis by taking advantage of subtract from, the energy....of the originalthesedifierences that I am able greatlyto sound impulse, while allowinga free passage for the escaping gas. To present this action clearly,recourse may be had to the analogous action occurring where a body ofliquid, such as water is suddenly released. Thus, in Fig. 1, I haverepresented a reservoir 1 opening by means of gates 2 into a channel 3having an unobstructed discharge. If the gates, now, be suddenly thrownopen, the height or weight of water in the reservoir representing thepotential energy of the body of escaping gas in the case of a motor,will first form a wall of water which will travel down the channel as atidal wave with a nearly perpendicular front; following this thehydraulic gradient, as determined by the continuous flow, will beestablished, the .tidal Wave meanwhile spreading at the discharge end ofthe channel. The

travel of such a tidal wave as that just described, requires no energybeyond that which starts it, this energy being passed from one moleculeto the next, as in a row of billiard balls, if the one on the end bestruck. Moreover, the energy of the wave being constant, as its frontgrows greater and greater, the energy is passed to a greater numberofmolecules, so that the amount of energy received by each successivemolecule grows correspondingly less. The motion of the molecules in thewave front itself, as such front passes down the channel, may beillustrated by assuming a body afloat as at B; it will remain at restuntil the movement of the tidal wave strikes it, because the velocity ofthe wave is limited only by the elasticity and density of the medium.When the water around the body receives the force of the wave, it is notinstantaneously able to escape on account of the inertia of the waterfarther down the channel, so it rises in height (pressure) and becomespart of the wave front, partaking of the forward motion of the latterand traveling in a path indicated in dotted outline in Fig. 2.

What it is desired to illustrate by the foregoing is that there is aregion of static energy forming the front of a wave impulse of thissort; also that the energy of the wave front is a constant after thewave has separated from the main discharge. These points of distinctionlead to diiferences between the mode of travel of an impulse in a fluidand a steady flow in that fluid; such, for instance, as that a soundwave has no momentum, but travels as readily at right angles to, as inthe original direction of flow; and is subject tono contraction whenpassing through a sharp-edged orifice. Pursuing the tidal wave analogyfurther, if it be assumed that the channel through which.

the wave passes is provided with a number of alternately projectingpiers 4 as shown in Fig. 3, it will be obvious that such wave willarrive at the mouth of the channel with as high a front except forenergy lost by friction and at the bends, as when it started. If,however, these pieces 4 should be pierced with a number of holes 5 andthe wave started down the channel as before, suchwave will lose aportion of its energy through the holes in the first of such piers, thenthrough those in the second and so on, so that when it passes around tothe lower side of each successive pier, the level there will alreadyhave been raised somewhat, and the energy of the wave front, asrepresented by its height, will be correspondingly decreased. Further,each little wave front as it progresses down the channel ahead of themain wave, is subjected to the same process of diminution, the generalresult being that the rise in pressure at the mouth of the channel isgradual and the spreading waves will be small, irregular and quicklydampened out. The applicability of this method of diminishing waveimpulses to the mufliing of the sound of a motor exhaust, may be bestunderstood from a reference to Fig. 4 of the drawings where I illustrateone approved construction of mufiler suited for use in connection withan ordinary automobile engine. As there shown, such muffler is outwardlyof the usual elongated cylindrical form, while internally it is formedinto a continuous spiral chamber 6 (see Fig. 4), that winds about theaxis of the mufiler so that the gases discharged into the center of themuffler will travel spirally about the center until they reach the outerportion 7 of such chamber, which opens at the farther end of the mufliersubstantially freely to the atmosphere through apertures 8. The walls ofthe spiral chamber are moreover pierced with numerous smallerperforations 9 similarly located in successive convolutions of saidchamber, so that in addition to the main impulse traveling spirallythrough the winding passage thus formed in the mufller, there will beformed a succession of smaller wave impulses that find their way throughthe series of openings 9. These smaller waves correspondinglydiminishing the main wave impulse, so that a gradual discharge resultsthrough the apertures 8 without any impediment being placed in the wayof the travel in the gases, but rather their escape being rendered freerby reason of the bypasses in the walls of the spiral passage.

In addition to the advantage obtained by the free exhaust, the foregoingconstruction allows .he escaping gas to retain nearly all of the kineticenergy of its discharge velocity which is obtained when the gas underpressure expands through the orifice of the exhaust valve of the engine.In other words, the gasis discharged from my improved silencer cool butat a high speed. By reason of such high speed and the high inertia ofthe gas, at the close of the disinches,

tion is perforated as at 18,

ordinary gas charge from the valve a considerable vacuum is caused atthe upper end of the exhaust pipe which, owing to the length of thepassage persists longer than where the velocity of the discharge hasbeen dampened by constrict'ion of the discharge orifice,,or theinterposition of actual barriers in the path of the discharge.

In Fig. 5 a helical passage is provided by arranging a partition 17 inthe form of a which partiscrew, within the mufller body,

in the same fashion as are the partitions construction shown in Fig. 4

The foregoing features of improvement, although apparently simple,.havebeen demonstrated in eliminate the noise of the explosions in the enginesuch as is used on automobiles and the like; so that, for example,withla minimum cross-sectional area of 7.5

the sound of the exhaust is. not audible to a passenger in the car abovethe ordinary noise. of the latter when running. At the same time thepower absorption is greatly reduced by providing a much freer outlet forthe escape of the exhaust gases.

Other modes of applyingthe principle of my inventionxmaybe employedinstead of the one explained, change being made as regards the mechanismherein disclosed, provided the means stated by any of the followingclaims -or the equivalent of such stated means be employed.

I therefore particularly point out and distinctly claim as myinvention 1. Apparatus for muflling sound, comprispassage, and a showninthe practice to almost entirely ing a chamberhaving an unobstructedspiral passage, and a plurality of openings disposed in the walls 9fsaid passage adapted to by-pass gases from said portion of such passageto a portion farther advanced, substantially as described.

2. Apparatus for mufiling sound, comprising a chamber having anunobstructed spiral plurality of openings disposed throughout the lengthof said spiral, passage adapted to successively by-pass gases from oneportion of such passage to a portion farther advanced,substantially asdescribed.

3. Apparatus for muflling sound, comprising a chamber having anunobstructed spiral passage adapted to receive the gases at one endthereof, and a plurality of openings in l the spiral walls disposedthroughout the length of said spiral passage and adapted to.successively by-pass gases from one portion to a portion fartheradvanced, substantially as described. f

4. Apparatus for muflling sound, comprising a cylindrical chamber havinga rod disposed centrally therein and a helical plate disposed about suchrod forming an unobstructed helical passage, said plate having aplurality of openings disposed throughout its length adapted to by-passgases from one portion of such passa e to a portion farther advanced,substantial y as described. I

Signed by me this 10th day of June, 1910.

- FRANK O. MOCK.

Attested by- ANNA L.- G JTNO. F. OBEZLJN.

